Monday, August 18, 2008

Here is the topology. I use this for a lot of NAT scenarios. I have a dynamips file all ready to go for it :) The frame-relay network is 172.12.123.x where x is the router number. You can use whatever internal routing method you want.

Requirements:

When R5 telnets to 172.12.123.1 it should go through R2.When R5 telnets to 172.12.123.1 port 3001 it should go through R3.

We will look at our NAT translations on R4 to verify.

First set up your outside interfaces (R4 to R2,R3) and inside interface (R4 to R5).

Not too bad, eh? NAT is still pretty initmadating for me. I can get easy scenarios out of the way, but some examples such as this still have the potential to cause me trouble. Hopefully, by practicing and doing these scenarios without any help, I can get it down pat...pun intended :)

2 comments:

I am not sure that your output interface is set based on the set statement in the route-map. I think the set interface is ignored for the purposes of NAT, and the source IP address of traffic is selected by interface line in the ip nat statement.

In other words, NAT correctly sets the source IP of traffic to the address of a specific interface, but that traffic will be forwarded out via routing. You could be forwarding traffic NATed to the IP of Fa0/0 out the Fa2/0 interface (and could receive responses on either interface, depending on routing).